We all know smoking is bad for your health. So is second-hand smoke. It turns out, even a leftover cigarette butt could be bad for you as well. Most butts are made with plastic and are not biodegradable. Scientists know nicotine and other toxins leach out of these ubiquitous plastic waste products, but recent research shows they could expose us to hazardous chemicals through an unexpected path — the air.

Each year, Americans buy more than 250 billion cigarettes, according to the Center for Disease Control. Many are tossed on the ground, making butts the most common type of litter on U.S. roads. As burnt cigarette butts pile up by the millions on beaches and streets all over the world, this new research could have big implications for those who live with smokers or deal with cigarette waste.

How did researchers figure this out and what does it mean for our health? Find out in an audio story narrated by Leto Sapunar. Music by Chad Crouch.

Narrator: There’s no dispute that smoking is bad for you. Exposure to firsthand, secondhand, and even thirdhand smoke — which is from the residues cigarette smoke leaves on objects — can impact your health. But what about the part of the cigarette that’s left behind AFTER smoking — the filter or butt? Until recently, researchers knew very little about what kind of chemicals discarded cigarette butts themselves emitted.

[lighter striking sound]

Poppendieck: If you think about cigarette butts, everybody knows kind of intuitively that they’re going to emit some chemicals even after they’ve been out, because you can sit on a park bench and you can smell that cigarette that’s been sitting next to the park bench on the ground, you can still smell that cigarette several hours later.

Narrator: That’s Dustin Poppendieck, an environmental engineer at the National Institute of Standards and Technology.

Poppendieck: And so we know that chemicals are coming off the cigarette butt. But what the real question was, was we didn’t know how fast and to what extent chemicals those come up… and how do they compare to when you’re actually actively smoking?

Narrator: Using a machine designed to simulate human smoking, Poppendieck and his team tested over 2000 cigarettes. They put the spent butts in enclosed containers and studied the gases that escaped, looking for eight chemicals on the FDA’s hazardous chemical list, including nicotine and triacetin — a chemical used to make the plastic in cigarette butts flexible. Initially skeptical, the team found that cigarette butts do emit a considerable amount of chemicals, some of which enter the air long after they’re extinguished. They published their findings in the journal Indoor Air.

Poppendieck: The ones that have a strong odor, they come off relatively quickly in the first six hours or so. So if you’re sitting at a park bench and you’re smelling a cigarette, it’s most likely somebody deposited it there in the last half day…

Narrator: But some chemicals stuck around a lot longer.

Poppendieck: But a couple of them, the triacetin and nicotine, are a little less volatile, meaning they don’t move out of the cigarette quite as fast as some of those other chemicals. And so they will continue to emit, for at least five days, probably…emitting for over four weeks.

Narrator: Poppendieck found that up to 14% of the nicotine released from smoking an entire cigarette was released from the butt itself over the course of a full day.

Poppendieck: So if you leave that cigarette butt in your car, you leave it in your house for five days, you can multiply that 14% by five, and now you’re starting to get up above half the nicotine mass is actually coming off the cigarette butt, as opposed to the act of smoking.

Narrator: Now Poppendieck says these numbers could help scientists figure out more realistic exposure levels to nicotine and other chemicals. One such scientist, Thomas Novotny is an epidemiologist at San Diego State University who studies the environmental impacts of tobacco. He also runs a non-profit that works to get rid of cigarette waste.

Novotny: Mostly what we’ve been looking at with cigarette butts as a waste product in the environment is what is exuded into the aquatic environment or even into soils. So what’s found in this study is an interesting sort of additional exposure pathway.

Nov: This just helps us further identify cigarette butts as a toxic hazardous waste product.

Narrator: Novotny says environmental groups involved in cigarette waste cleanup activities can be exposed to millions of butts at a time.

Nov: I think it’s clear that people who handle these, whether intentionally or by accident or even commercially, need to be protected in terms of their toxic potentials.

Narrator: Poppendieck only studied one brand of cigarettes and is hesitant to jump to broad conclusions from these findings.

Poppendieck: Cigarettes burn very differently depending on the type of paper. Projecting this to other cigarette brands and types is difficult. I wouldn’t say that the numbers would project definitely at all. But I would say that the general trend, you’d probably see the same general trends where you would see some persistence of the nicotine and triacetin chemicals and the other chemicals falling off relatively quickly.

Narrator: After so much time studying them, Poppendieck can’t help but look at cigarette butts differently.

Poppendieck: I didn’t realize how prevalent they were until we did the study and you can pretty much walk down any sidewalk that has like a cutout for a tree in any urban center. Anytime you see that tree, you’ll pretty much see a cigarette butt…I was at a conference talking about this topic in Europe last year, and I walked down one side of the city block and there were over 350 cigarette butts on that sidewalk and you can’t see them…you can’t not see them anymore.